1. Field of the Invention
The present invention relates to novel nitroprotein markers for lung damage caused by smoke exposure, and to methods identifying people vulnerable to developing Chronic Obstructive Pulmonary Disease (COPD) and related respiratory conditions using such a marker. The present invention also relates to therapeutic methods for targeting such a nitroprotein to prevent and treat respiratory disease.
2. Discussion of the Background
Chronic Obstructive Pulmonary Disease (COPD) is a disease of the lungs in which the airways become narrowed and the patient experiences shortness of breath. The limitation of airflow is poorly reversible and usually worsens over time.
The prevalence and associated mortality of COPD have increased dramatically in recent years, due in large part to cigarette smoking. It is projected to be the third leading cause of death worldwide by 2020. Noxious particles in smoke trigger an inflammatory response in the lung, leading to destruction of alveolar tissue, a condition known as emphysema. The inflammatory response in the larger airways is known as chronic bronchitis, which is diagnosed clinically when sputum is coughed up.
Cigarette smoke is a complex mixture of substances including oxidants and nitrosants such as nitric oxide that may initiate the inflammatory response in the lung. Alveolar macrophages, neutrophils, CD8+ lymphocytes, other inflammatory cells and airway epithelial cells generate and release reactive oxygen species (ROS) such as the superoxide anion (O2−), hydrogen peroxide (H2O2), and the hydroxyl radical (OH−) through an NADPH-oxidase-dependent mechanism. These cells can also generate nitric oxide (NO−) free radical through a nitric oxide synthase (NOS)-dependent mechanism. Inducible NOS (iNOS) can generate large amounts of NO for an extended period of time during an inflammatory response. Most of the cellular toxic effects of NO result from its rapid reaction with O2− to form the strong nitrosant peroxynitrite anion (ONOO−). Peroxynitrite causes the nitration (addition of —NO2) of a protein tyrosine residue. Tyrosine nitration can compromise protein structure and function, the impact mainly being on the structural and conformation properties of proteins and their potential signalling and catalytic activities.
Detection and quantification of total nitrotyrosine in biological samples has been conducted using anti-nitrotyrosine antibodies and by HPLC. The results have confirmed that smokers have higher degrees of protein nitration than non-smokers (Zhang W Z et al. Biomed. Chromatogr., 2007, 21(3): 273-8), and that tyrosine nitration is considerably increased in the lung tissue of patients with ARDS (adult respiratory distress syndrome) relative to non-ARDS controls (Haddad et al. J. Clin. Invest., 94: 2407-2413, 1994).
The prior art does not describe any analysis of individual protein nitration in lung disease, nor diagnostic measures for COPD dependent on selectively detecting and analysing individual nitroproteins or nitropeptides in a biological sample.
Currently COPD is diagnosed by lung function tests such as spirometry, or procedures such as blood tests, chest X-rays and Computed Tomography (CT) scans.
To a certain degree the condition can be controlled by lifestyle changes such as cessation of smoking, nutrition, exercise and avoidance of air pollution. However, to date there are no pharmacologic therapies that can reduce the decline in lung function that characterizes COPD, although the symptoms can be managed with systemic corticosteroids and bronchodilators.
Part of the difficulty in developing treatments for COPD is that although there are many candidate COPD biomarkers (e.g. sputum neutrophils, interleukin (IL)-8, and tumor necrosis factor-α), there is a lack of validated lung-specific biomarkers that can be used as an intermediate end point for clinical trials. Biomarkers can be defined as indicators associated with a particular disease or condition where there is a correlation between the presence or level of the biomarker and some aspect of the disease or condition. One important criterion for a COPD biomarker is that it should have biological plausibility in terms of its role in pathogenesis of the disease. Recently, C-reactive Protein (CRP) was proposed as blood-based marker for COPD, but it has since been discredited because it is a general, rather than lung-specific marker for systemic inflammation (Sin and Man, Chest, 2008; 133; 1296-1298).
Thus, there is an urgent need to identify new, preferably lung-specific biomarkers that can allow physicians to monitor the stage of advancement of COPD and its associated underlying physiological changes.